The RNA sequencing technique will be adapted to the analysis of polyribonucleotides at low molar concentrations by investigating the incorporation of radioactive labels into the nucleoside fragments that are successively removed by the periodate-beta-elimination procedure. The study of the synthesis and properties of polynucleotides containing ribo-deoxyribo hybrid sequences will be undertaken. A new approach to the chemical synthesis of polynucleotides on solid supports will be investigated.